Described herein are steer-by-wire systems and methods of operating these systems in vehicles. A steer-by-wire system comprises a steering wheel assembly, comprising a steering wheel, sensors, and a torque generator. The system comprises a rack assembly, comprising a steering rack, sensors, and a rack actuator. The steering wheel assembly and the rack assembly are communicatively coupled by a steer-by-wire system controller, without having any direct mechanical links between the assemblies. In some examples, the controller instructs the rack assembly to control the steering rack position based on the steering input, such as changes in the steering wheel position. A steering map is used to determine the desired steering rack position based on the current steering wheel position. In some examples, a steering map is selected from a steering map set based on, e.g., the vehicle speed, vehicle direction, driver preference, and the like.
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1. A vehicle comprising:
a vehicle network;
a first communication link;
a second communication link; and
a steer-by-wire system comprising a steering wheel controller configured to control one or more components of a steering wheel assembly, the steering wheel controller communicatively coupled to the vehicle network using the first communication link and communicatively coupled separately to the vehicle network using the second communication link, wherein:
the steering wheel controller comprises a first steering wheel electronic control unit (ecu) communicatively coupled to the vehicle network using the first communication link,
the steering wheel controller further comprises a second steering wheel ecu communicatively coupled to the vehicle network using the second communication link and communicatively coupled separately to the first steering wheel ecu using a steering wheel internal-communication bus (ICB), and
the first steering wheel ecu, the second steering wheel ecu, and the steering wheel ICB are configured such that switching between the first communication link and the second communication link does not require switching between the first steering wheel ecu and the second steering wheel ecu.
2. The vehicle of
3. The vehicle of
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7. The vehicle of
a first steering rack ecu communicatively coupled to the first steering wheel ecu using the first communication link; and
a second steering rack ecu communicatively coupled to the second steering wheel ecu using the second communication link and communicatively coupled separately to the first steering rack ecu using a steering rack ICB, and
wherein the first steering rack ecu, the steering rack ICB, and the second steering rack ecu are configured such that switching between the first communication link and the second communication link does not require switching between the first steering rack ecu and the second steering rack ecu.
8. The vehicle of
9. The vehicle of
10. The vehicle of
11. The vehicle of
12. The vehicle of
13. The vehicle of
14. The vehicle of
15. The vehicle of
receive sensor measurements related to an angular position of a steering wheel of the steering wheel assembly from a steering wheel position sensor; and
receive sensor measurements related to a torque applied to the steering wheel by a driver from a steering wheel torque sensor.
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the first steering wheel ecu is configured to operate as a primary steering wheel ecu;
the first steering wheel ecu is configured to receive input data over the first communication link; and
in response to the input data not being received over the first communication link or the input data being received more reliably over the second communication link, the first steering wheel ecu is configured to receive the input data from the second communication link via the second steering wheel ecu without the second steering wheel ecu switching to operate as the primary steering wheel ecu.
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This application is a continuation of U.S. patent application Ser. No. 17/336,513, filed on Jun. 2, 2021, which is a continuation of U.S. patent application Ser. No. 17/200,033 filed on Mar. 12, 2021 and granted as U.S. Pat. No. 11,052,940 on Jul. 6, 2021, both of which are incorporated herein by reference in their entirety for all purposes.
Conventional steering systems utilize direct mechanical links between the steering wheels and road wheels (e.g., front steerable wheels). These links are used to translate the steering input to the turning of road wheels while maintains the steering alignment, which is the alignment between the steering wheels and the corresponding steerable road wheels. This steering system type will be referred to as a mechanically-linked system to differentiate it from other types of steering systems that do not have such mechanical links.
Unlike mechanically-linked systems, steer-by-wire systems do not have such mechanical links between their steering wheels and road wheels. While this lack of mechanical connection presents some challenges (e.g., maintaining the steering alignment), it also provides new design and operating opportunities, in comparison to mechanically-linked systems. For example, the steering wheels and the road wheels can be independently controlled to provide improved vehicle operations across different driving conditions (e.g., different speeds, driving in reverse, and the like) and integration of new vehicle systems (e.g., autonomous driving). Furthermore, this lack of mechanical connection opens door to new positions of the steering wheel in a vehicle, independent from the position of steering wheels, thereby greatly increase flexibility in cabin packaging.
Described herein are steer-by-wire systems and methods of operating these systems. A steer-by-wire system comprises a steering wheel assembly and a rack assembly. The steering wheel assembly comprises a steering wheel, sensors, and an actuator. The rack assembly comprises a steering rack, sensors, and a rack actuator. The two assemblies are communicatively coupled by a steer-by-wire system controller, which may comprise two sub-controllers, without having any direct mechanical links between the assemblies. In some examples, the controller instructs the rack assembly to control the steering rack position based on the steering input, such as changes in the steering wheel position. For example, a steering map is used to calculate the steering rack position target based on the current steering wheel position. In some examples, a steering map is selected from a steering map set based on, e.g., the vehicle speed, vehicle direction, driver preference, and the like.
The description will be more fully understood with reference to the following figures, which are presented as examples of the disclosure and should not be construed as a complete recitation of the scope of the disclosure, wherein:
In the following description, numerous specific details are outlined to provide a thorough understanding of the presented concepts. In some examples, the presented concepts are practiced without some or all of these specific details. In other instances, well-known process operations have not been described in detail so as not to unnecessarily obscure the described concepts. While some concepts will be described in conjunction with the specific examples, it will be understood that these examples are not intended to be limiting.
A steer-by-wire system presents various new design options as well as vehicle operating options, which are not possible with conventional mechanically-linked steering systems. By removing the mechanical link, the steer-by-wire system enables various independent controls of the steering wheel and the road wheels. For example, the road wheels are turned using the steering rack. The steering rack position is controlled based on the steering wheel position, e.g., using specially designed steering maps. The same steering map may have multiple steering rack position options for the same steering wheel position. One of these steering rack position options is selected or, more specifically, interpolated (e.g., using an interpolation function) based on one or more additional factors (e.g., vehicle speed). As a result, both the vehicle controllability (e.g., at high speeds) and the vehicle responsiveness (e.g., at low speeds) can be independently controlled across various operating conditions.
A brief description of a steer-by-wire system is presented below with reference to
Steer-by-wire system 110 is configured to receive the power from multiple power sources (e.g., first power source 106 and second power source 107). For example, first power source 106 and second power source 107 may be two independent low-voltage batteries (e.g., 12V batteries, 48V batteries). In some examples, one or more power sources may be a high-voltage battery (e.g., 400V-800V batteries in electrical vehicles) connected to steer-by-wire system 110 through a DC-DC power converter. Other examples include a capacitor (e.g., as a temporary power source) and the like.
Referring to
Steering wheel controller 112 and rack controller 116 are configured to communicate with each other, e.g., to synchronize the operation of steering wheel assembly 140 and rack assembly 150. Furthermore, steering wheel controller 112 and rack controller 116 are configured to communicate with vehicle network 105. First communication link 101 and second communication link 102 may be used for various types of communications within vehicle 100.
Steering wheel controller 112 comprises first steering wheel ECU 113 and second steering wheel ECU 114. The two ECUs ensure the continuous operation of steer-by-wire system 110, e.g., if one ECU becomes unavailable. Steering wheel controller 112 also comprises steering wheel internal-communication bus (ICB) 115, communicatively coupling and providing a direct communication link between first steering wheel ECU 113 and second steering wheel ECU 114. As such, first steering wheel ECU 113 and second steering wheel ECU 114 may redundantly communicate internally within steering wheel controller 112 (using steering wheel ICB 115) and/or externally (using first communication link 101 and second communication link 102 and one or more ECUs in vehicle network 105 as a gateway). For example, first steering wheel ECU 113 may be communicatively coupled to first communication link 101, while second steering wheel ECU 114 may be communicatively coupled to second communication link 102.
Rack controller 116 comprises first steering rack ECU 117 and second steering rack ECU 118, e.g., to ensure continuous operation if one of the ECU becomes unavailable. Rack controller 116 comprises rack ICB 119, communicatively coupled and providing a direct communication link between first steering rack ECU 117 and second steering rack ECU 118. As such, first steering rack ECU 117 and second steering rack ECU 118 may communicate internally within rack controller 116 (using rack ICB 119) and/or externally (e.g., using first communication link 101 and second communication link 102 and one or more ECUs in vehicle network 105 as a gateway). For example, first steering rack ECU 117 may be communicatively coupled to first communication link 101, while second steering rack ECU 118 may be communicatively coupled to second communication link 102.
Steering wheel 141 is used by driver 190 to provide steering input. For example, driver 190 rotates steering wheel 141, thereby changing the angular position of steering wheel 141, to control the driving direction of vehicle 100. The angular position of steering wheel 141 is registered by steering wheel position sensor 146 and transmitted to steering wheel controller 112.
Steering wheel absolute position limiters 142 are mechanical components, which come in contact with corresponding components on steering wheel 141 when steering wheel 141 is rotated to some degree (e.g., from the center position). Steering wheel absolute position limiters 142 determine absolute steering wheel limits 122, which may be also referred to as mechanical steering wheel limits. Absolute steering wheel limits 122 are schematically shown in
Steering wheel actuator 144 may be an electrical motor, coupled to steering wheel 141 (e.g., using a steering column). Steering wheel actuator 144 is operable to rotate steering wheel 141, e.g., to control steering wheel position 120. In some examples, steering wheel actuator 144 is also operable to apply a set torque to steering wheel 141, e.g., based on various maps and features described below, provided as instructions from steering wheel controller 112.
In some examples, steering wheel actuator 144 is configured to set tunable steering wheel limits 124. Referring to
Steering wheel position sensor 146 is configured to measure changes in the angular position of steering wheel 141. For example, steering wheel position sensor 146 may be positioned on a steering column, which supports steering wheel 141. Similarly, steering wheel torque sensor 147 is configured to measure the torque applied by driver 190 to steering wheel 141. For example, steering wheel torque sensor 147 may be positioned on a steering column, which supports steering wheel 141. In some examples, steering wheel position sensor 146 and steering wheel torque sensor 147 may be integrated into the same hardware components.
Now referring to the components of rack assembly 150, steering rack 151 is mechanically coupled to road wheels 191 and is used to change the angle of road wheels 191 thereby allowing vehicle 100 to turn. Steering rack 151 is mechanically coupled to rack actuator 154, which is used to change the position of steering rack 151, e.g., based on the input from rack controller 116.
Rack absolute position limiters 152 are mechanical components, which come in contact with corresponding components of steering rack 151 thereby limiting the position of steering rack 151 and the angle of road wheels 191. Rack absolute position limiters 152 determine the maximum travel of steering rack 151 and may be referred to as mechanical rack limits.
Rack actuator 154 is mechanically coupled to rack assembly 150 and is used to change the position of rack assembly 150, e.g., between rack absolute position limiters 152. Rack actuator 154 may include an electrical motor or an electrical linear actuator. Referring to
Rack position sensor 156 is configured to measure changes in the position of steering rack 151. For example, rack position sensor 156 may be positioned on or integrated into steering rack 151 and/or rack actuator 154. Similarly, rack force sensor 157 is configured to estimate or measure the force with which road wheels 191 affect the movement of steering rack 151. Rack force sensor 157 may be positioned on or integrated into steering rack 151 and/or can be estimated by measuring related measurements, such as current and position.
Some examples of data flow in steer-by-wire system 110 are illustrated in
Steering wheel position 120 is then used to determine or, more specifically, to calculate steering rack position target 138 based on steering map 170. Steering rack position target 138 is then transmitted to rack actuator 154, e.g., to move steering rack 151. This procedure may be performed in reverse as well if there is the movement of the rack due to external forces. Rack position sensor 156 measures and returns steering rack position 130 to one or more controllers, such as steering wheel controller 112. A combination of steering rack position 130 and steering rack position target 138 may be used to determine rack position difference 135, used for various functions described below and schematically shown in
As described above with reference to
Referring to
Returning to
In some examples, method 200 comprises (block 210 in
In some examples, method 200 also comprises (block 211) obtaining vehicle direction 108, e.g., from vehicle network 105. The vehicle direction may be a part of the vehicle speed signal, e.g., from a wheel speed sensor. For example, the sign of the vehicle speed signal (e.g. positive for forward, negative for reverse) may indicate the direction. In some examples, the vehicle direction is computed from a set of separate signals (e.g., the gear selection (P-R-N-D), powertrain motor torque direction).
In some examples, method 200 comprises, when (decision block 212) steering wheel position 120 is at or above one of tunable steering wheel limits 124, applying (block 214) resistive torque 164 to steering wheel 141. As further described above with reference to
This sub-process may involve checking if tunable steering wheel limit 124 exists for vehicle speed 109, obtained earlier. If this tunable steering wheel limit 124 exists, then method 200 proceeds with checking if steering wheel position 120 is at tunable steering wheel limit 124 or exceeds this tunable steering wheel limit 124. If tunable steering wheel limit 124 is reached or exceeded, then a resistive torque is applied to inhibit further rotation of steering wheel 141 in that direction.
Method 200 proceed with (block 220 in
Method 200 then proceeds with (block 230) controlling steering rack position 130 based on steering rack position target 138. For example, steering wheel controller 112 instructs rack actuator 154 to move steering rack 151 based on steering rack position target 138, e.g., as schematically shown in
Referring to
When the vehicle direction 108 is a separate input, one of the steering rack position values 173 is further selected based on the vehicle direction, in addition to vehicle speed 109 and steering wheel position 120 as further described below. For example, steering map 170 may have a specific set of steering rack position values 173, corresponding to the reverse movement as shown in
Two subsets of steering wheel position values 172 and corresponding steering rack position values 173 in steering map 170 are presented graphically in
In some examples, steering wheel controller 112 (or steering wheel position sensor 146) can retain steering wheel position 120 only while the power is supplied to steering wheel controller 112 (or steering wheel position sensor 146). More specifically, steering wheel controller 112 can retain steering wheel calibrated reference 125, which may be referred to as an absolute steering wheel angle reference or an absolute reference. As noted above, steering wheel calibrated reference 125 is then combined with steering wheel position sensor input 126, which may be referred to as a relative angle, to obtain steering wheel position 120. Steering wheel controller 112 then uses steering wheel position 120 to calculate steering rack position target 138, which is sent to rack actuator 154 to change steering rack position 130.
As such, when no power is supplied to steering wheel controller 112 (or steering wheel position sensor 146), e.g., while vehicle batteries are removed or discharged below a set threshold, steering wheel calibrated reference 125 may be lost and steering wheel position 120 cannot be determined. Furthermore, steering wheel 141 may be turned without steering wheel position sensor 146 being able to register the change in steering wheel position 120 (e.g., if steering wheel 141 is rotated while vehicle 100 is switched off and steer-by-wire system 110 is unpowered). Such situations may be referred to as a loss of steering wheel calibrated reference 125 as, as a result, a loss of the steering wheel's absolute angle.
Without steering wheel position 120, the operation of steer-by-wire system 110 will be limited. For example, steering map 170 uses steering wheel position 120 to select steering rack position value 173, which is used to control steering rack position 130. Finally, periodic calibration of steering wheel position 120 may be needed or the process may be triggered externally (e.g., as a part of vehicle maintenance).
In some examples, method 400 commences with steering wheel controller 112 determining (block 410 in
Method 400 proceeds with sending (block 414 in
Method 400 proceeds with steering wheel controller 112 receiving (block 416 in
Method 400 proceeds with rotating (block 420 in
If driver torque 149 exceeds the driver-torque threshold (decision block 424, “NO” arrow), method 400 may proceed with warning (block 468) driver 190 to remove obstacles from steering wheel 141. Alternatively, steering wheel 141 is rotated until steering wheel actuator torque 166 reaches the actuator-torque (decision block 426, “NO” arrow), at which point method 400 proceed with registering (block 430) first temporary steering wheel position 491. First temporary steering wheel position 491 is a steering wheel position at which, during the calibration process, steering wheel actuator torque 166 reaches or exceeds actuator-side torque threshold 167. It should be noted that first temporary steering wheel position 491 may correspond to one of absolute steering wheel limits 122 or some intermediate obstruction point. At this stage of method 400, Steering wheel controller 112 is not able to distinguish between this absolute steering wheel limit and the potential obstruction point. As such, first temporary steering wheel position 491 cannot yet be assigned as steering wheel position 120.
Method 400 proceeds with rotating (block 440 in
Method 400 proceeds with determining (block 460 in
Method 400 then proceeds with comparing (decision block 462 in
As noted above, steering wheel position 120 is a combination of steering wheel position sensor input 126 and steering wheel calibrated reference 125. In the above example, second temporary steering wheel position 492 represents steering wheel position sensor input 126 when steering wheel 141 is at one of steering wheel absolute position limiters 142. However, steering wheel controller 112 stores the information, representing steering wheel position 120 at each of steering wheel absolute position limiters 142. Steering wheel controller 112 uses this information to calculate an offset between second temporary steering wheel position 492 and steering wheel position 120 and determine steering wheel calibrated reference 125.
Furthermore, based on the now determined steering wheel position 120, method 400 proceeds with rotating (block 466) steering wheel 141 until steering wheel position 120 matches steering rack position 130. For example, steering wheel position 120, corresponding to steering rack position 130, may be determined inversely using steering map 170 as further described below. It should be noted that, in some examples, steering rack position 130 does not change during various operations of method 400. In other words, mechanical aspects of method 400 are performed by steering wheel assembly 140. In some examples, method 400 also comprises sending (block 467 in
Alternatively, when temporary steering wheel position range 493 is less than absolute steering wheel rotation range 123, then at least one of absolute steering wheel limits 122 was not reached during the previous rotation operations. As such, it is not possible to conclude that the current position of steering wheel 141, e.g., second temporary steering wheel position 492, is at the one absolute steering wheel limits 122. In this case, method 400 may proceed with sending (block 468 in
In some examples, steer-by-wire system 110 is configured to support the overall vehicle operation at rare and unintended operating conditions, For example, a power interruption to one or more components of steer-by-wire system 110 may occur or vehicle 100 is incorrectly activated/immobilized while steer-by-wire system 110 has not yet completed the calibration process. In these rare operating conditions, steering wheel position 120 or, more specifically, steering wheel calibrated reference 125 may not be available even if vehicle 100 is not fully immobilized. For purposes of this disclosure, immobilization may be referred to as a vehicle state at which vehicle 100 is not in motion and cannot start moving. It should be noted that steering wheel position sensor 146 may remain operational and provide steering wheel position sensor input 126. However, this steering wheel position sensor input 126 may not be used to produce steering wheel position 120 since steering wheel calibrated reference 125 is not available.
When vehicle 100 is not immobilized, a process of determining steering wheel position 120, which is described above with reference to method 400 cannot be used. Specifically, uninterrupted steering input from driver 190 may be needed when vehicle 100 is not stationary as conditions around vehicle 100 can change. In these examples, steer-by-wire system 110 is operated in a special steering mode, which may also cause the entire vehicle 100 to operate in a limp mode. This special steering mode allows driver 190 to continue providing the steering input and to operate vehicle 100, e.g., to bring vehicle 100 to a stop. When vehicle 100 is immobilized, steering wheel position 120 may be reestablished in accordance with method 400 described above.
Method 500 proceeds with steering wheel controller 112 obtaining (block 520) steering rack position 130. For example, steering rack position 130 is obtained by rack position sensor 156 and first transmitted to rack controller 116, which then transmits steering rack position 130 to steering wheel controller 112. It should be noted that steering rack position 130 represents the current position of steering rack 151.
Method 500 then proceeds with steering wheel controller 112 calculating (block 525) temporary steering wheel uncalibrated reference 129, based on current steering rack position 130 as, e.g., is schematically shown in
Method 500 proceeds with steering wheel controller 112 monitoring (block 532) steering wheel position sensor input 126 as, e.g., is schematically shown in
Referring to
Alternatively, when steering wheel torque 161 is less than steering wheel torque threshold 162 (decision block 555), method 500 proceeds determining (block 570) temporary steering wheel position 127 from temporary steering wheel uncalibrated reference 129 and steering wheel position sensor input 126. This operation is similar to obtaining steering wheel position 120 from steering wheel calibrated reference 125 and steering wheel position sensor input 126. Method 500 also proceeds with selecting (block 572) steering rack position target 138 based on temporary steering wheel position 127 and transmitting (block 574) steering rack position target 138 to rack actuator 154. Specifically, steering rack position target 138 is selected using steering map 170.
In some examples, method 500 involves updating temporary steering wheel uncalibrated reference 129 based on steering rack position target 138 obtained based on steering wheel torque 161. For example, when steering rack 151 is allowed to move while steering wheel 141 does not rotate, the temporary reference changes. This process may be referred to as intermediate calibration.
Method 500 repeats in cycles as shown in
As noted above, steering rack position 130 is changed using rack actuator 154, e.g., based on steering rack position target 138 received from steering wheel controller 112. Rack actuator 154 has a maximum rate with which steering rack position 130 can be changed for a given rack force. This rate may be referred to as a maximum rack movement speed. The maximum rack movement speed depends on the power of rack actuator 154 and the resistive force operable on steering rack 151. Furthermore, as noted above, steering map 170 defines the relationship between steering rack position 130 and steering wheel position 120 or, more specifically, between steering rack position values 173 and steering wheel position values 172. As such, the maximum rack movement speed has a corresponding steering wheel turning speed, which may be referred to as a maximum allowable steering wheel rotation. If driver 190 turns steering wheel 141 faster than the maximum allowable steering wheel rotation, then rack actuator 154 may not able to change steering rack position 130 fast enough, resulting in the misalignment of steering rack position 130 and steering wheel position 120. In other words, in this example, steering rack position 130 lags behind steering wheel position 120. This phenomenon is also referred to as catch-up.
Method 600 proceeds with determining (block 612) steering wheel rotation speed 143 based on changes in steering wheel positions 120. In some examples, steering wheel rotation speed 143 is determined directly from multiple steering wheel position sensor input 126, e.g., without first determining steering wheel positions 120. In some examples, method 600 also involves calculating steering rack position target 138 based on steering wheel positions 120, e.g., using steering map 170. Steering rack position target 138 may be used later to determine the alignment between steering wheel 141 and steering rack 151, e.g., by comparing steering rack position target 138 to steering rack position 130.
Method 600 then proceeds with obtaining (block 620) steering rack position 130 from rack position sensor 156. Method 600 also involves determining (block 630) the steering rack speed from changes in steering rack position 130.
In some examples, method 600 comprises obtaining (block 640) vehicle speed 109 and/or obtaining (block 642) the rack force. The rack force is applied by rack actuator 154 and may be, e.g., measured by rack force sensor 157 or estimated from the current flowing to rack actuator 154.
Method 600 proceeds with selecting (block 650) resistive torque target 168 based on steering wheel rotation speed 143 and/or other parameters presented in steering feedback resistive torque map 165, one example of which is shown in
Other factors include steering wheel speed, rack speed, rack force, and vehicle speed. Steering feedback resistive torque map 165 comprises steering wheel rotation speed values, to which steering wheel rotation speed 143 is compared. Furthermore, steering feedback resistive torque map 165 comprises resistive torque target values, corresponding to different steering wheel rotation speed values. In some examples, steering feedback resistive torque map 165 comprises other values, such as rack position difference values and vehicle speed values, which are further described below.
During the design/calibration phase, the power characteristics of rack actuator 154 are known. The rack force is also continuously measured (e.g., using rack force sensor 157) or calculated (e.g., from the current flow to rack actuator 154). Therefore, the resistive torque target values in steering feedback resistive torque map 165 may be specifically tuned to prevent catch-up using the rack force. For example, higher resistive torque target values may be used for resisting driver's efforts, characterized by steering wheel rotation speed/rate. In some examples, the steering wheel rotation speed, attempted by driver 190, may be greater than the capabilities of rack actuator 154 to move steering rack 151, in which case higher resistive torque target values are selected from steering feedback resistive torque map 165.
In some examples, resistive torque target 168 is selected using steering feedback resistive torque map 165 and based on the rack force, the steering wheel rotation speed, the vehicle speed, and the rack speed. For example, steering feedback resistive torque map 165 comprises the rack force and the rack speed, corresponding to the steering wheel speed and the vehicle speed, which may result in a target resistive torque value, e.g., tuned to prevent catch-up.
Method 600 proceeds with transmitting (block 660) resistive torque target 168 to steering wheel actuator 144. In turn, steering wheel actuator 144 uses resistive torque target 168 to control the torque, which driver 190 experiences as driver 190 tries to turn steering wheel 141.
In some examples, various issues may occur with the alignment between steering wheel 141 and steering rack 151. For example, steering wheel 141 may be rotated while vehicle 100 is switched off with the respective controllers not registering this rotation. The realignment process depends, at least in part, on the immobilization status of vehicle 100. Specifically, when vehicle 100 is moving (e.g., vehicle speed 109 is not equal to zero), the alignment needs to occur as soon as possible. On the other hand, when vehicle 100 is stationary (e.g., vehicle speed 109 is at or close to zero), moving steering rack 151 and, as result, turning road wheels 191 (without any input from or awareness of driver 190) in the stationary vehicle may cause unintended consequences (e.g., contacting with an object proximate to road wheel 191). Overall, moving steering rack 151 and, as a result, road wheels 191 should be avoided without driver control and intent while vehicle 100 is stationary. In some examples, steer-by-wire system 110 is configured to perform different alignment operations depending on vehicle speed 109 as will now be described with reference to
Method 700 proceeds with determining (block 720) rack position difference 135 based on steering wheel position 120 and steering rack position 130. For example, steering wheel position 120 may be used together with steering map 170 to determine steering wheel position target 128. The difference between steering wheel position target 128 and steering rack position 130 may be used as rack position difference 135, which indicates the alignment level in steer-by-wire system 110.
Method 700 proceeds with comparing (decision block 725) rack position difference 135 with one or more thresholds, such as first alignment threshold 177. For example, when rack position difference 135 (decision block 725) is greater than first alignment threshold 177, then the alignment may be needed. Method 700 may also involve checking (decision block 735) if the vehicle propulsion is allowed (e.g., vehicle 100 may be already moving or may be authorized to move by vehicle network 105). In this situation, the vehicle will enter limp mode however a quick alignment may still need to be performed. Specifically, when the vehicle propulsion is allowed (decision block 725), method 700 proceeds with determining (block 740) at least one of steering wheel position target 128 and/or steering rack position target 138 calculated in such a way as to realign steering wheel and rack position as quickly as possible. This determination operation is performed based on rack position difference 135. For example, steering alignment map 175 may be used in this operation. One example of steering alignment map 175 is presented in
Method 700 then returns to the previous operations of obtaining (block 710) steering wheel position 120 and obtaining (block 715) steering rack position 130.
When the vehicle propulsion is not allowed (decision block 735), method 700 proceeds with rack position difference 135 (decision block 745) is greater than second alignment threshold 178. Second alignment threshold 178 is greater than first alignment threshold 177. The purpose of first alignment threshold 177 is to determine if the alignment is necessary at all. The purpose of second alignment threshold 178 is to determine if the alignment level is such that driver 190 and, in some examples, vehicle network 105 need to be informed. Specifically, when rack position difference 135 (decision block 745) is less than second alignment threshold 178, method 700 proceed with determining (block 760) steering wheel position target 128. It should be noted that steering rack position target 138 is not determined when the vehicle propulsion is not allowed and the alignment is performed only by rotating steering wheel 141 (and not moving steering rack 151). Steering wheel position target 128 is determined based on rack position difference 135 and, for example, using steering alignment map 175.
When rack position difference 135 (decision block 745) is greater than second alignment threshold 178, method 700 proceed with sending (block 750) a steering system update (e.g., a system calibration request) to vehicle network 105 and receiving (block 752) a response from vehicle network 105 before proceeding with determining (block 760) steering wheel position target 128.
In some examples, steering wheel 141 does not include a mechanical lock (“M-lock”) or an electronic steering lock (“E-lock”), e.g., for reasons such as packaging, costs, and the like. At the same time, drivers 190 often use steering wheel 141 as support during the vehicle ingress or egress. In a conventional steering system, where the mechanical lock is provided or where the steering wheel is mechanically coupled to the road wheels, the movement of the steering wheel is restricted by this lock or the road wheels. For example, the road wheels are difficult to move while the vehicle is stationary if the system is unpowered.
Method 800 commences with receiving (block 810) driver status input 194 from one or more vehicle network 105. Driver status input 194 may include various information, such as (1) driver 190 entering vehicle 100; (2) driver 190 inside vehicle 100; (3) driver 190 exiting vehicle 100; (4) driver 190 outside vehicle 100; and (5) driver's state unknown. Vehicle network 105 generates driver status input 194 based on feedback from various sensors and systems in vehicle 100. For example, sensing the wireless key outside vehicle 100 may be an indication that driver 190 is planning to enter vehicle 100. A seat sensor may indicate that driver 190 is inside vehicle 100. When driver 190 is inside vehicle 100 and also when vehicle 100 is being turned off may be used to determine that driver 190 is planning to leave vehicle 100. Overall, vehicle network 105 collect various information from vehicle 100 (e.g., door status, seatbelt status, steering hands-on/hands-off detection, actuation of any controls (e.g., gear, pedals, switches), seat sensors, interior and/or exterior camera, wireless access car detection, phone Bluetooth connection, and the like) and uses this information to determine driver status input 194, which is supplied to steering wheel controller 112 as schematically shown in
In some examples, one or more parameters are separately analyzed by steering wheel controller 112. For example, method 800 may comprise verifying (decision block 812) the vehicle speed. If the speed is not zero (and vehicle 100 is in motion), method 800 is not performed. Similarly, method 800 may comprise verifying (decision block 814) the gear selection. If the gear selection is not “park” (P), method 800 is also not performed.
Returning to
More specifically, during this resistive torque applying operation, steering wheel controller 112 sends resistive torque instruction 193 to steering wheel actuator 144 as schematically shown in
As soon as driver status input 194 changes (e.g., to other states not corresponding to driver 190 entering or exiting vehicle 100), resistive torque 164 is removed (block 840). The removal of resistive torque 164 allows, for example, to turn steering wheel 141, e.g., during operation of vehicle 100. In some examples, resistive torque 164 is removed gradually (e.g., in case driver 190 rests on steering wheel 141 and still relies on steering wheel 141 for support). This gradual removal of resistive torque 164 prevents the steering wheel from snapping.
It should be noted that the alignment between steering wheel 141 and steering rack 151 is controlled even when resistive torque 164 is applied to steering wheel 141. For example, driver 190 may be able to overcome resistive torque 164 and turn steering wheel 141, in which case steering rack 151 also changed its position to maintain the alignment.
Referring to
In general, switching between communication links and/or ECUs is based on operation criticality, component unavailability, and other factors. The overall approach is to maintain the current ECU even while linking to a different communication link where more reliable data may be available for some sensors or vehicle inputs unless the change in both is unavoidable to maintain the vehicle operation. It should be noted that when an ECU switch is performed, one level of redundancy is lost and may no longer available for future operations.
For example, a vehicle speed is used for various operations of steer-by-wire system 110, such as steering map lookup, controlling power-up/down, and the like. If the vehicle speed is missing on first communication link 101, steer-by-wire system 110 may obtain the vehicle speed on second communication link 102. This operation is performed without switching to a redundant ECU and without switching other signals to second communication link 101, e.g., only the vehicle speed is obtained through second communication link 102. Furthermore, if the vehicle speed is not available through either communication link, then steer-by-wire system 110 defaults to a safe tuning map that does not require the vehicle speed input. In another example, if steering wheel position sensor 146 is not able to provide output, the output is received from additional steering wheel position sensor 946. This new output may be used by first steering wheel ECU 113 and communicated to first steering wheel ECU 113 through second steering wheel ECU 114 and steering wheel ICB 115. Other sensors (e.g., steering wheel torque sensor 147 and additional steering wheel torque sensor 947) may have the same redundancy.
Furthermore, multiple ECUs in each assembly allow supporting the operation of this assembly, when once ECU becomes unavailable, without impacting any other systems. For example, first steering wheel ECU 113 may become unavailable to support some operations and steering wheel controller 112 switches to second steering wheel ECU 114. Communication to vehicle network 105 may be still provided using first communication link 101, e.g., through first steering wheel ECU 113 and steering wheel ICB 115. Furthermore, second steering wheel ECU 114 may support components of steering wheel assembly 140 (previously supported using first steering wheel ECU 113), such as steering wheel position sensor 146 and steering wheel torque sensor 147. In other words, steering wheel assembly 140 can maintain additional steering wheel position sensor 946 and additional steering wheel torque sensor 947 in reserve.
In another example, steering wheel assembly 140 may switch from steering wheel position sensor 146 to additional steering wheel position sensor 946 without impacting any other operations, e.g., continue using first steering wheel ECU 113. The connection to additional steering wheel position sensor 946 is provided by second steering wheel ECU 114 and steering wheel ICB 115. The same approach applies to steering wheel torque sensor 147 and additional steering wheel torque sensor 947.
It should be noted that the communication between first steering wheel ECU 113 and second steering wheel ECU 114 may be through steering wheel ICB 115 or, independently, through first communication link 101, vehicle network 105, and second communication link 102. Various examples described above with reference to steering wheel controller 112 are also applicable to steering rack controller 116. For example, sensor communication redundancies apply to rack position sensor 156, rack force sensor 157, additional steering rack position sensor 956, and additional rack force sensor 957 shown in
Furthermore, various cross-communications are possible between steering wheel ECUs and steering rack ECUs. For example, first steering wheel ECU 113 may communicate with first steering rack ECU 117 using first communication link 101. In another example, first steering wheel ECU 113 may communicate with second steering rack ECU 118 using a combination of first communication link 101, first steering rack ECU 117, and steering rack ICB 119. Other communication options are also within the scope.
Finally, if a component becomes available again, steer-by-wire system 110 allows restoring communication to this component.
In some examples, steer-by-wire system 110 is configured to collect various system performance data. This data may be transmitted for an external analysis (e.g., across a fleet of vehicles, across vehicles of the same model, etc.) or used for internal analysis by vehicle 100. For example, this steer-by-wire system performance data may be used to change various steering and/or torque maps described above (e.g., to limit the occurrence of undesired behavior), to determine various service and maintenance intervals (e.g., premature wear of some components), to study driving habits and system utilization (e.g., parking maneuvers), to update steering systems of an autonomous vehicle, and cost-saving opportunities.
One example of the steer-by-wire system performance data is an alignment log, which may be maintained by steering wheel controller 112. For example, Steering wheel controller 112 records occurrences of a rack position difference exceeding a set threshold (e.g., more than 2 mm). As noted above, a rack position difference is determined based on steering rack position 130 and steering wheel position 120 or, more specifically, is determined as a difference between steering rack position 130 and steering rack position target 138, identified based on steering wheel position 120, e.g., using steering map 170. The occurrences of a rack position difference are recorded, e.g., when steer-by-wire system 110 is operating in the normal mode (based on the status at Steering wheel controller 112, Rack controller 116, and vehicle network 105).
In some examples, multiple instances of a rack position difference are grouped, e.g., over a set period (e.g., 10 seconds), and the highest value of a rack position difference is recorded from this group. Some examples of the data corresponding to a rack position difference include, but are not limited to, the different value and sign, the vehicle speed at the time, steering wheel position 120 at the time, steering wheel rotation speed 143 at the time, steering wheel torque at the time, an estimated force acting on steering rack 151, vehicle mileage at the time, and date-time of the event.
In some examples, steering wheel controller 112 monitors the time duration and mileage between software flashes and also in total for the steering unit. For example, steering wheel controller 112 may monitor the vehicle travel distance (e.g., based on the internal data or data received from vehicle network 105, such as an odometer module). This travel distance may be used to set service intervals and other functions.
In some examples, steering wheel controller 112 monitors the following events: (1) a number of times steering wheel controller 112 has entered a reduced mode (e.g., one or more vehicle systems have been subject temperatures, voltages, and/or other conditions outside of the operating range), (2) a number of times rack controller 116 has entered a reduced mode, (3) a number of times steering wheel controller 112 has triggered the reduced mode, (4) a number of times rack controller 116 has triggered the reduced mode, (5) a number of faults affecting primary system, causing a switch to secondary ECUs, (6) a number of latent faults affecting secondary path, (7) a number of times the catch-up module has been activated (e.g., below a set speed) or, more specifically, a number of times the target and actual rack position was greater than a given threshold, (8) a number of times a curb condition has been detected, (9) a number of times an alignment has been required at power-up due to a misalignment between actual rack position and demanded rack position greater than a threshold (e.g., 10 mm), (10) a number of times the resistive torque has been exceeded, (11) a number of times a belt slip event in rack controller 116 has been detected, (12) a number of times various steering features have been activated, and the like.
Although the foregoing concepts have been described in some detail for purposes of clarity of understanding, it will be apparent that some changes and modifications may be practiced within the scope of the appended claims. It should be noted that there are many alternative ways of implementing the processes, systems, and apparatus. Accordingly, the present examples are to be considered as illustrative and not restrictive.
Narasimhan, Ganesh, Pucci, Paolo E.
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